As is known in the art, NEXRAD radar sites perform elevation scans at various angles to collect weather-related data. FIG. 1 illustrates the various elevation angles that a NEXRAD radar site may scan and the range for each scan angle. NEXRAD radar sites may experience interference caused by the radar detecting electromagnetic radiation from another source, most often another radar or the Sun. The Sun particularly poses problems near sunrise and sunset at elevation scan angles approximately equal to the angle of the Sun. The interference generally corrupts one or more radials of radar data, and particularly affects most or all of a radial, usually out to the maximum range. Such interference from the Sun is known in the art as a “Death Ray,” which will be used herein to mean false echoes that occur near sunrise and sunset which are caused by solar radiation. Examples of the false echoes are shown in FIGS. 2 and 3, as “Death Rays” 10, 12, 14, 16 and 18.
A problem is that NEXRAD radar data provided by the National Weather Service does not contain any logic to detect and/or correct for interference from the Sun. The problem is so large that over 300 of the NEXRAD 0.5 degree Base Reflectivity products are affected by the Death Ray effect each day. The number increases if all NEXRAD elevation scans are included. This problem results in degraded radar products, as is evidenced by FIGS. 2 and 3, where the inclusion of the Death Rays 10, 12, 14, 16 and 18 makes the product more difficult to interpret.
Another problem is that radials are wider as they go out in range (e.g., the radials look similar to a baseball bat, with the narrow end towards the radar and the fat end pointing at the source of contamination). Thus, it is likely that real echoes will be embedded within the false echoes. When interference is encountered, the reflectivity values increase with range, with a maximum being about 35 dBZ. The interference appears for one or two volume scans for a single elevation and up to 30 minutes on a Composite Reflectivity product. Other reflectivity derived products, such as echo tops, layer reflectivity and composite reflectivity are also affected. Still further, radial velocity and spectrum width products usually indicate range-aliased data, and due to radial velocity corruption, the mesoscale process can be negatively affected.
Yet another problem is that many of the NEXRAD site clocks are not synchronized to a standard time, thus making the calculation of the Sun's position less accurate. Thus, without a certain time reference, automatic identification and removal of the Death Ray is difficult as the Sun's position relative to the particular radar scan cannot be accurately determined.
Given the right tools and time, a trained Meteorologist can manually identify and remove the false echoes. This is the approached used by providers such as WSI of Billerica, MA for their NOWrad product which is available every 15 minutes. However, there is a significant drawback to this method as it delays the release of the product for up to 7 minutes. This is a significant amount of time, especially when there is fast changing weather. As a result, for more timely products, such as WSI's 5-Minute NOWrad PLUS and Premium NOWrad, manual removal is not practical.
Thus, there is a need for a system of automatic removal of Death Ray effects that can be quickly and automatically performed. In addition, there is a need for a system of automatic removal of Death Ray effects that is very accurate and does not remove real echoes. The present invention provides for such a system.